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VOLCANOES OF THE LOWER OLD RED SANDSTONE book v 
the bedded andesites, and that it is in turn traversed by dykes composed of 
a material indistinguishable from that of some of the flows. He therefore 
considered tliat it is essentially of the same age as the rest of the volcanic 
series, and “ not improbably the deep-seated source of it.” ^ Mr. Teall also, 
from a chemical and microscopical examination of the rocks, drew a similar 
conclusion.^ 
The andesites around the granite liave undergone contact-metamorphism, 
but the nature and extent of the change have not yet been studied. There 
occur around the granite many dykes of felsite and quartz-felsite, to the 
petrographical character of which reference has already been made. But 
the most abundant and remarkable dykes of the district are those of a 
reddish mica-porphyrite, of which Mr. Clough has mapped no fewer than 
forty, besides those in the granitic area. He has called attention to the 
signiflcant manner in which all the dykes of tlie district tend to point in a 
general way to the great core of granite, as if that were the nucleus from 
which they had radiated.^ 
The central granite of the Cheviot Hills, with its peripheral dykes, has 
no accompanying agglomerates nor any decided proof that it ever com- 
municated with the surface. When, however, we consider its petrograpliical 
and chemical constitution, its position as a core among the bedded lavas, 
and the intimate way in which it is linked with these rocks by the net- 
work of dykes, we are, I think, justified in accepting the inference that it 
belongs to the volcanic series. It possesses some cuilous and interesting 
features in common witli the great granophyre bosses of Tertiary age in 
the Inner Hebrides. Like these it has no visible accompaniment of 
superficial discharges. Yet it may have ascended by means of some central 
vent or group of vents which, offering to it a weak part of the crust, 
allowed it to communicate with tlie surface and give rise to the outflow of 
lavas and fragmental ejections. In any case, it affords us a most interesting 
and instructive insight into one of the deeper-seated ducts of a volcanic 
region, and the relation of a volcanic focus to the ascent of the granitic 
magma. 
About twenty miles to the north of the Cheviot Hills, and separated 
from them by the Carboniferous and Upper Old Bed Sandstones which 
spread across the broad plain of the Merse, a group of volcanic rocks has 
been laid open in a singularly instructive manner along the coast of 
Berwickshire, between the village of Eyemouth and the promontory of St. 
Abb’s Head. Xot only the actual vent.s, but the lavas and tuffs connected 
with them, have there been admirably dissected l)y the forces of denudation. 
That this volcanic area was cprite distinct from that of the Cheviot 
Hills may be inferred from its coarse agglomerates, and from the fact tliat 
when the rocks are followed inland in a south-westerly direction, that is, 
towards the Cheviot area, they are found to diminish in thickness and to 
disappear among the ordinary sediments. For the same reason we may 
1 Op. cit. p. 24. 2 Geol. May. 1885, p. 106. ® Op. cit. pp. 26-28. 
